Mobile terminals such as mobile phones and mobile information terminals have rapidly diffused with the development of mobile communication systems. Smaller and more sophisticated mobile terminals have been developed. In addition, the number of frequency bands employed in a single mobile terminal has steadily increased due to, for example, the diffusion of Long Term Evolution (LTE). Acoustic wave devices are used for filters and duplexers provided to devices employed in the mobile terminals. As the acoustic wave device, employed is a Surface Acoustic Wave (SAW) device, a boundary acoustic wave device, or a Bulk Acoustic Wave (BAW) resonator.
Japanese Patent Application Publication No. 7-99420 discloses providing a shield layer in a substrate on which a chip including an acoustic wave element formed therein is mounted.
The provision of the shield layer in the substrate enables to reduce the leakage of a high-frequency signal from the chip. However, the shield layer and the ground of the acoustic wave chip are interconnected in the substrate in Japanese Patent Application Publication Nos. 7-99420 and 2003-273520. Thus, a high-frequency signal leaks from the chip through the ground.